linux-kernel - Re: [PATCH 2/2] arm64: efi: Pass reboot cmd parameter to efi

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Message-ID: <CAMj1kXE60LrWi8Au6qQ4EMQDFxQCJt5h6hBLuQHCz3HEp=2o3w@mail.gmail.com>
Date: Fri, 14 Nov 2025 10:35:33 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Sumit Garg <sumit.garg@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-efi@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, catalin.marinas@....com, will@...nel.org, 
	mark.rutland@....com, andersson@...nel.org, konradybcio@...nel.org, 
	dmitry.baryshkov@....qualcomm.com, shivendra.pratap@....qualcomm.com, 
	leif.lindholm@....qualcomm.com, linux-kernel@...r.kernel.org, 
	Sumit Garg <sumit.garg@....qualcomm.com>
Subject: Re: [PATCH 2/2] arm64: efi: Pass reboot cmd parameter to efi_reboot()

On Fri, 14 Nov 2025 at 10:33, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Fri, 14 Nov 2025 at 10:31, Sumit Garg <sumit.garg@...nel.org> wrote:
> >
> > On Fri, Nov 14, 2025 at 10:26:03AM +0100, Ard Biesheuvel wrote:
> > > On Fri, 14 Nov 2025 at 09:51, Sumit Garg <sumit.garg@...nel.org> wrote:
> > > >
> > > > From: Sumit Garg <sumit.garg@....qualcomm.com>
> > > >
> > > > EFI ResetSystem runtime service allows for platform specific reset type
> > > > allowing the OS to pass reset data for the UEFI implementation to take
> > > > corresponding action. So lets pass the reboot cmd parameter for the EFI
> > > > driver to determine whether it's a platform specific reset requested or
> > > > not.
> > > >
> > > > Signed-off-by: Sumit Garg <sumit.garg@....qualcomm.com>
> > > > ---
> > > >  arch/arm64/kernel/process.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > > > index fba7ca102a8c..51784986c568 100644
> > > > --- a/arch/arm64/kernel/process.c
> > > > +++ b/arch/arm64/kernel/process.c
> > > > @@ -136,7 +136,7 @@ void machine_restart(char *cmd)
> > > >          * ResetSystem().
> > > >          */
> > > >         if (efi_enabled(EFI_RUNTIME_SERVICES))
> > > > -               efi_reboot(reboot_mode, NULL);
> > > > +               efi_reboot(reboot_mode, cmd);
> > > >
> > >
> > > I agree with the general principle. However, there are already
> > > existing callers of kernel_restart() that would end up passing a
> > > random string to efi_reboot(), resulting in platform specific reset
> > > with undefined result.
> >
> > Yeah true but the UEFI spec says:
> >
> > "If the platform does not recognize the EFI_GUID in ResetData the platform
> > must pick a supported reset type to perform. The platform may optionally
> > log the parameters from any non-normal reset that occurs."
> >
> > So, in these cases the UEFI implementation can fallback to normal reset
> > optionally logging the reset data being passed. Does that sounds
> > reasonable to you?
> >
>
> What the UEFI spec says might deviate from how real platforms in the
> field will behave when being passed a reset type that nobody ever
> tried passing before.

Also, the GUID is expected to follow an unbounded NULL terminated
UTF-16 string in memory, so we could easily cause a crash by doing
this if \0\0 doesn't appear in the memory following the string.